Determination of the Levels of Heavy Metals in Surface Water, Tilapia Fish ( Oreochromis Niloticus ) and Soil Within the Vicinity of Oil Production Facilities During Wet and Dry Season in Omoku, Rivers State

value, whereas a value greater than 1 indicates enrichment or contamination above the reference level. Pollution Load Index The Pollution Load Index was used to determine the overall level of heavy-metal pollution resulting from the combined effects of the metals investigated. The PLI was calculated as the geometric mean of the contamination factors: PLI=(CF1×CF2×CF3×⋯×CFn)1/n Where (CF1, CF2 to CFn) are the contamination factors for the individual heavy metals and (n) is the number of metals assessed. A PLI value < 1 indicates no overall pollution, while a PLI value > 1 indicates an overall pollution load relative to the selected reference concentrations. The BAF, CF and PLI values were calculated separately for the wet and dry seasons and for Obrikom River (Onosi Ognu), Onosi Okpasimini and Control station to evaluate spatial and seasonal variations in heavy-metal accumulation and pollution. Results Table 1: Heavy metal concentrations in water during wet season Heavy metals (mg/L) Obrikom River (Onosi Ognu) Onosi Okpasimini Control DPR LIMIT Pb 1.70±0.00 2.49±0.010 1.10±0.00 0.15 Cu 5.86±0.00 7.15±0.00 2.73±0.06 36 Cr 5.17±0.04 6.52±0.00 2.17±0.00 1.6 Cd 0.05±0.00 0.17±0.00 0.002±0.00 0.10 Ni 4.32±0.00 3.03±0.00 1.723±0.05 2.7 Fe 72.58±0.00 66.03±0.13 45.19±0.23 50 IJCCP , Table 2: Heavy metal concentrations in water during dry season Heavy Metals (mg/L) Obrikom River (Onosi Ognu) Onosi Okpasimini Control DPR Limit Pb 2.18 ± 0.02 2.86 ± 0.01 1.24 ± 0.01 0.15 Cu 6.73 ± 0.05 8.24 ± 0.03 3.18 ± 0.04 36 Cr 6.14 ± 0.03 7.31 ± 0.02 2.64 ± 0.01 1.6 Cd 0.08 ± 0.00 0.21 ± 0.01 0.003 ± 0.00 0.10 Ni 4.86 ± 0.02 3.57 ± 0.01 1.94 ± 0.04 2.7 Fe 79.64 ± 0.12 73.58 ± 0.15 48.76 ± 0.21 50 Table 3: Heavy metal concentration in Tilapia fish (Oreochromis niloticus) during Wet Season Heavy Metals (mg/kg) Obrikom River (Onosi Ognu) Onosi Okpasimini Control DPR Limit Pb 2.84 ± 0.06 3.62 ± 0.08 1.18 ± 0.03 0.30 Cu 4.76 ± 0.11 5.83 ± 0.14 2.21 ± 0.05 30.00 Cr 3.94 ± 0.09 4.87 ± 0.12 1.73 ± 0.04 1.00 Cd 0.46 ± 0.02 0.61 ± 0.03 0.08 ± 0.01 0.20 Ni 2.73 ± 0.07 3.18 ± 0.09 1.24 ± 0.04 1.00 Fe 48.63 ± 0.82 56.74 ± 0.96 32.18 ± 0.61 100.00 Table 4: Heavy metal concentrations in Tilapia fish (Oreochromis niloticus) during dry Season Heavy Metals (mg/kg) Obrikom River (Onosi Ognu) Onosi Okpasimini Control DPR Limit Pb 3.41 ± 0.08 4.26 ± 0.11 1.39 ± 0.04 0.30 Cu 5.38 ± 0.13 6.72 ± 0.16 2.54 ± 0.06 30.00 Cr 4.71 ± 0.11 5.68 ± 0.14 2.08 ± 0.05 1.00 Cd 0.57 ± 0.03 0.76 ± 0.04 0.10 ± 0.01 0.20 Ni 3.16 ± 0.08 3.79 ± 0.10 1.47 ± 0.04 1.00 Fe 54.72 ± 0.91 64.83 ± 1.04 35.46 ± 0.68 100.00 Table 5: Heavy metal concentrations in soil during wet Season Heavy Metals (mg/kg) Obrikom River (Onosi Ognu) Onosi Okpasimini Control DPR Limit Pb 18.42 ± 0.31 24.67 ± 0.42 8.36 ± 0.18 85 Cu 21.36 ± 0.27 28.54 ± 0.35 12.18 ± 0.21 36 Cr 31.74 ± 0.46 38.62 ± 0.51 16.43 ± 0.29 100 Cd 0.72 ± 0.04 1.08 ± 0.06 0.21 ± 0.02 0.80 IJCCP , Heavy Metals (mg/kg) Obrikom River (Onosi Ognu) Onosi Okpasimini Control DPR Limit Ni 17.63 ± 0.32 22.48 ± 0.39 9.72 ± 0.17 35 Fe 684.35 ± 8.42 758.62 ± 9.17 421.58 ± 6.73 1000 Table 6: Heavy metal concentrations in soil during dry Season Heavy Metals (mg/kg) Obrikom River (Onosi Ognu) Onosi Okpasimini Control DPR Limit Pb 22.76 ± 0.38 29.83 ± 0.47 9.64 ± 0.21 85 Cu 25.84 ± 0.32 33.76 ± 0.41 13.47 ± 0.24 36 Cr 36.82 ± 0.51 44.73 ± 0.58 18.76 ± 0.33 100 Cd 0.86 ± 0.05 1.27 ± 0.07 0.25 ± 0.02 0.80 Ni 20.48 ± 0.36 26.73 ± 0.43 10.84 ± 0.19 35 Fe 742.63 ± 9.14 826.47 ± 10.26 458.72 ± 7.18 1000 Table 7: Bioaccumulation Factor of Heavy Metals in Oreochromis niloticus During Wet Season Heavy Metals Obrikom River (Onosi Ognu) Onosi Okpasimini Control Pb Cu 1.67 0.81 1.45 0.82 1.07 0.81 Cr 0.76 0.75 0.80 Cd 9.20 3.59 40.00 Ni 0.63 1.05 0.72 Fe 0.67 0.86 0.71 Table 8: Bioaccumulation Factor of Heavy Metals in Oreochromis niloticus During Dry Season Heavy Metals Obrikom River (Onosi Ognu) Onosi Okpasimini Control Pb 1.56 1.49 1.12 Cu 0.80 0.82 0.80 Cr 0.77 0.78 0.79 Cd 7.13 3.62 33.33 Ni 0.65 1.06 0.76 Fe 0.69 0.88 0.73 IJCCP , Table 9: Contamination Factor (CF) and Pollution Load Index of Heavy Metals in Water During Wet Season Heavy Metals Obrikom River (Onosi Ognu) Onosi Okpasimini Control Pb 11.33 16.60 7.33 Cu 0.16 0.20 0.08 Cr 3.23 4.08 1.36 Cd 0.50 1.70 0.02 Ni 1.60 1.12 0.64 Fe 1.45 1.32 0.90 PLI 1.38 1.80 0.45 Table 10: Contamination Factor (CF) and Pollution Load Index of Heavy Metals in Water During Dry Season Heavy Metals Obrikom River (Onosi Ognu) Onosi Okpasimini Control Pb 14.53 19.07 8.27 Cu 0.19 0.23 0.09 Cr 3.84 4.57 1.65 Cd 0.80 2.10 0.03 Ni 1.80 1.32 0.72 Fe 1.59 1.47 0.98 PLI 1.70 2.08 0.54 Table 11: Contamination Factor (CF) and Pollution Load Index of Heavy Metals in Soil During Wet Season Heavy Metals Obrikom River (Onosi Ognu) Onosi Okpasimini Control Pb 0.22 0.29 0.10 Cu 0.59 0.79 0.34 Cr 0.32 0.39 0.16 Cd 0.90 1.35 0.26 Ni 0.50 0.64 0.28 Fe 0.68 0.76 0.42 PLI 9.88 12.75 4.81 Table 12: Contamination Factor (CF) and Pollution Load Index of Heavy Metals in Soil During Dry Season Heavy Metals Obrikom River (Onosi Ognu) Onosi Okpasimini Control Pb 0.27 0.35 0.11 Cu 0.72 0.94 0.37 Cr 0.37 0.45 0.19 IJCCP , Heavy Metals Obrikom River (Onosi Ognu) Onosi Okpasimini Control Cd 1.08 1.59 0.31 Ni 0.59 0.76 0.31 Fe 0.74 0.83 0.46 PLI 11.59 14.88 5.44 Heavy Metal Concentrations in Water, Tilapia Fish and Soil The results presented demonstrate clear spatial and seasonal variations in the concentrations of heavy metals in surface water, Oreochromis niloticus and soil within the study area. The metals investigated were led (Pb), copper (Cu), chromium (Cr), cadmium (Cd), nickel (Ni) and iron (Fe). In general, the concentrations recorded at Onosi Okpasimini were higher than those observed at Obrikom River (Onosi Ognu), whereas the Control station generally recorded the lowest concentrations. This spatial pattern suggests that the two impacted locations are exposed to greater inputs or accumulation of metal contaminants than the Control location. The finding is environmentally important because recent investigations in Nigerian aquatic ecosystems have similarly demonstrated substantial spatial heterogeneity in heavy-metal concentrations among sampling stations, with locations influenced by anthropogenic activities generally recording greater contamination than reference locations (Ujah et al., 2025). Heavy Metals in Surface Water During Wet Season Table 4.9 shows that Pb concentrations during the wet season ranged from 1.10 ± 0.00 mg/L at the Control station to 2.49 ± 0.010 mg/L at Onosi Okpasimini, while Obrikom River recorded 1.70 ± 0.00 mg/L. All three stations therefore exceeded the stated DPR limit of 0.15 mg/L. Onosi Okpasimini recorded approximately 16.6 times the stated limit, while Obrikom River and the Control station recorded approximately 11.3 and 7.3 times the limit, respectively. The particularly elevated Pb concentration at Onosi Okpasimini indicates that Pb represents one of the major contaminants of concern in the surface water. The elevated concentration may be associated with anthropogenic inputs such as petroleum-related activities, vehicular emissions, industrial discharges, waste disposal, corrosion of metallic materials and runoff from contaminated areas. Lead is persistent in aquatic systems and may be transported in dissolved form or associated with suspended particles before eventually becoming incorporated into bottom deposits. The present Pb concentrations are notably high when compared with a recent investigation of Biu Reservoir, Nigeria, where Wakil et al. (2025) reported Pb concentration of 0.016 mg/L in reservoir water and identified the elevated Pb concentration as a potential environmental and health concern. The Pb concentrations in the present study are therefore considerably higher than those reported for Biu Reservoir, suggesting a comparatively stronger Pb burden in the studied water bodies. Similarly, Boma and Nwoke (2026), in a recent investigation of the Bonny River in Rivers State, reported a mean Pb concentration of 3.23 ± 1.11 mg/L in surface water and classified Pb as exhibiting a very high degree of contamination based on contamination-factor assessment. The Pb concentrations observed in the present study, particularly at Onosi Okpasimini, are therefore within the same broad order of magnitude as those recently reported from another Niger Delta aquatic system. This similarity strengthens the interpretation that Pb contamination remains an important environmental issue in petroleum-influenced aquatic ecosystems of southern Nigeria. Copper concentrations during the wet season ranged from 2.73 ± 0.06 mg/L at the Control station to 7.15 ± 0.00 mg/L at Onosi Okpasimini, with Obrikom River recording 5.86 ± 0.00 mg/L. IJCCP , Although the concentrations were considerably higher at the impacted stations than at the Control station, all values remained below the stated DPR limit of 36 mg/L. The approximately 2.6-fold difference between Onosi Okpasimini and the Control station indicates substantial spatial enrichment even though the concentrations did not exceed the regulatory benchmark. Copper may originate from both natural weathering and anthropogenic sources, including industrial activities, petroleum operations, metallic infrastructure, domestic wastewater and surface runoff. The fact that Onosi Okpasimini recorded the highest concentration suggests that localised sources may be contributing to Cu loading in that location. Chromium concentrations ranged from 2.17 ± 0.00 mg/L at the Control station to 6.52 ± 0.00 mg/L at Onosi Okpasimini, while Obrikom River recorded 5.17 ± 0.04 mg/L. All measured concentrations were substantially higher than the stated DPR limit of 1.6 mg/L. Onosi Okpasimini therefore recorded approximately four times the regulatory value, whereas Obrikom River recorded more than three times the limit. The elevated Cr concentrations may reflect inputs from industrial activities, petroleum-related processes, metal- containing wastes and weathering of chromium-bearing materials. Chromium is particularly important from an environmental-health perspective because its toxicity depends strongly on its chemical form, with hexavalent chromium generally being substantially more toxic than trivalent chromium. Therefore, where only total chromium was analysed, the present results should be interpreted as evidence of total Cr contamination rather than as direct evidence of Cr(VI) toxicity. The wet-season Cd concentration was 0.05 ± 0.00 mg/L at Obrikom River, 0.17 ± 0.00 mg/L at Onosi Okpasimini and 0.002 ± 0.00 mg/L at the Control station. Onosi Okpasimini consequently exceeded the stated DPR limit of 0.10 mg/L, while Obrikom River remained below the limit. The very low concentration at the Control station provides additional evidence of a spatially localised Cd input. Cadmium is particularly significant because it is non-essential to biological systems and can accumulate in aquatic organisms. The recent Bonny River study by Boma and Nwoke (2026) also reported Cd in surface water and classified Cd as exhibiting a very high degree of contamination. The similarity is particularly relevant because the Bonny River and the present study area are both situated within the Niger Delta environmental setting. Nickel concentrations ranged from 1.723 ± 0.05 mg/L at the Control station to 4.32 ± 0.00 mg/L at Obrikom River, with Onosi Okpasimini recording 3.03 ± 0.00 mg/L. Obrikom River and Onosi Okpasimini exceeded the stated DPR limit of 2.7 mg/L, whereas the Control station remained below the limit. The distribution differs slightly from Pb, Cu, Cr and Cd because Obrikom River recorded the highest Ni concentration rather than Onosi Okpasimini. This suggests that the sources and environmental behaviour of Ni may differ from those of the other metals. Nickel can enter aquatic environments through petroleum activities, industrial discharges, combustion processes, metal corrosion and natural mineral weathering. Iron recorded the highest absolute concentrations among all metals investigated, with values of 72.58 ± 0.00 mg/L at Obrikom River, 66.03 ± 0.13 mg/L at Onosi Okpasimini and 45.19 ± 0.23 mg/L at the Control station. The concentrations at Obrikom River and Onosi Okpasimini exceeded the stated DPR limit of 50 mg/L, while the Control station was slightly below the limit. The relatively high Fe concentration may partly reflect natural geochemical contributions because iron is abundant in many soils and sediments; however, the higher concentrations at the impacted locations indicate that anthropogenic contributions cannot be excluded. Ujah et al. (2025) similarly observed substantial Fe concentrations in the River Niger ecosystem and reported that the highest Fe concentration in water was associated with the site that also showed the highest Fe accumulation in fish. IJCCP , The wet-season water results show that Pb and Cr were consistently elevated at all sampling locations relative to the stated DPR limits, while Cd and Ni showed exceedances at selected impacted stations and Fe exceeded the stated limit at the two main study stations. Cu was the only metal among those investigated that remained below the stated regulatory limit at all locations. This pattern indicates that the water body is subject to multiple-metal contamination rather than contamination by a single element. Heavy Metals in Surface Water During Dry Season The dry-season results in Table 4.10 show a general increase in the concentrations of most metals compared with the wet-season results. Pb increased from 1.70 to 2.18 mg/L at Obrikom River, from 2.49 to 2.86 mg/L at Onosi Okpasimini and from 1.10 to 1.24 mg/L at the Control station. These represent increases of approximately 28.2%, 14.9% and 12.7%, respectively. The continued exceedance of the DPR limit at all stations indicates persistent Pb contamination throughout the year rather than a short-lived wet-season phenomenon. The dry-season increase in Pb is environmentally plausible because reduced river flow and lower dilution during the dry period can increase the concentration of contaminants in the water column. Furthermore, continued inputs from anthropogenic sources during periods of reduced rainfall can result in greater apparent concentrations. Similar spatial and environmental variability has been reported in recent Nigerian aquatic studies, where heavy-metal concentrations varied considerably among sites according to the intensity and proximity of contaminant sources (Ujah et al., 2025; Yusuf et al., 2025). Copper increased during the dry season to 6.73 ± 0.05 mg/L at Obrikom River, 8.24 ± 0.03 mg/L at Onosi Okpasimini and 3.18 ± 0.04 mg/L at the Control station. Although these concentrations remained below the stated DPR limit of 36 mg/L, the consistent increase relative to the wet-season values indicates seasonal concentration of Cu. The highest dry-season concentration at Onosi Okpasimini further confirms that this location experienced greater metal loading than the Control station. Chromium increased from 5.17 to 6.14 mg/L at Obrikom River, from 6.52 to 7.31 mg/L at Onosi Okpasimini and from 2.17 to 2.64 mg/L at the Control station. Consequently, Cr remained above the stated regulatory limit at all three locations. The persistence of elevated Cr in both seasons indicates that chromium contamination is not merely a consequence of rainfall-driven runoff but may also involve continuous or residual sources within the catchment. Cadmium increased from 0.05 to 0.08 mg/L at Obrikom River and from 0.17 to 0.21 mg/L at Onosi Okpasimini, while the Control concentration increased only slightly from 0.002 to 0.003 mg/L. The dry-season Cd concentration at Onosi Okpasimini was therefore more than twice the stated DPR limit. The strong difference between the impacted and Control locations suggests that Cd is particularly associated with local anthropogenic inputs. This observation agrees with the 2026 Bonny River investigation, which identified Cd as one of the metals contributing substantially to water contamination in the Niger Delta. Nickel increased at Obrikom River from 4.32 to 4.86 mg/L and at the Control station from 1.723 to 1.94 mg/L, whereas Onosi Okpasimini increased from 3.03 to 3.57 mg/L. The dry-season concentrations remained above the stated DPR limit at Obrikom River and Onosi Okpasimini. Iron also increased from 72.58 to 79.64 mg/L at Obrikom River, from 66.03 to 73.58 mg/L at Onosi Okpasimini and from 45.19 to 48.76 mg/L at the Control station. Thus, the dry-season Fe concentrations at the two impacted stations remained above the stated limit. The overall dry-season results therefore demonstrate a stronger heavy-metal burden than during the wet season. This seasonal pattern is important because it indicates that periods of reduced dilution may increase the exposure of aquatic organisms to dissolved and suspended metals. However, seasonal variation should not be attributed solely to dilution; changes in runoff, IJCCP , sediment resuspension, pH, redox conditions, organic matter and metal partitioning between water and solid phases may also influence the measured concentrations. Heavy Metal Concentrations in Oreochromis niloticus During Wet Season The results for tilapia in Table 11 demonstrate that heavy metals present in the water were also reflected in fish tissues. Pb concentrations were 2.84 ± 0.06 mg/kg at Obrikom River, 3.62 ± 0.08 mg/kg at Onosi Okpasimini and 1.18 ± 0.03 mg/kg at the Control station. All three values exceeded the stated DPR limit of 0.30 mg/kg. Onosi Okpasimini therefore recorded approximately 12 times the stated limit, while Obrikom River recorded approximately 9.5 times the limit. The elevated Pb concentration in fish is particularly important because fish occupy an important position in aquatic food webs and may transfer accumulated contaminants to human consumers. The present finding is consistent with recent research in Nigeria. Wakil et al. (2025), studying Biu Reservoir, detected Pb and Cd contamination in fish and reported Cd in O. niloticus gills above the applicable safety limit. Similarly, Boma and Nwoke (2026), working in the Bonny River, reported Pb and Cd concentrations in tilapia above applicable limits. The agreement between these studies and the present results provides strong evidence that Pb accumulation in edible or biologically relevant fish tissues remains a significant concern in Nigerian aquatic systems. Copper concentrations in the tilapia ranged from 2.21 ± 0.05 to 5.83 ± 0.14 mg/kg, with all values below the stated permissible limit of 30 mg/kg. Although Cu did not exceed the fish-tissue limit, the concentration at Onosi Okpasimini was more than twice that of the Control station. This spatial pattern suggests uptake from the surrounding aquatic environment. Copper is an essential trace element at low concentrations but can become toxic when environmental exposure is excessive. Chromium concentrations ranged from 1.73 ± 0.04 mg/kg at the Control station to 4.87 ± 0.12 mg/kg at Onosi Okpasimini. All three stations exceeded the stated limit of 1.00 mg/kg. The elevated Cr concentrations indicate that the contamination observed in the water was accompanied by transfer into fish tissue. Recent research by Ogunbanwo et al. (2025) specifically investigated heavy-metal bioaccumulation in O. niloticus and Chrysichthys nigrodigitatus from Sagbo Koji, Lagos, demonstrating the usefulness of fish tissues as indicators of aquatic heavy-metal contamination. Cadmium showed particularly notable accumulation in tilapia, with concentrations of 0.46 ± 0.02 mg/kg at Obrikom River and 0.61 ± 0.03 mg/kg at Onosi Okpasimini, compared with only 0.08 ± 0.01 mg/kg at the Control station. The two impacted locations therefore exceeded the stated permissible limit of 0.20 mg/kg. The substantially higher Cd concentration in fish from Onosi Okpasimini corresponds with its higher Cd concentration in water, demonstrating an apparent environmental transfer relationship. Nickel concentrations in fish were 2.73 ± 0.07 mg/kg at Obrikom River, 3.18 ± 0.09 mg/kg at Onosi Okpasimini and 1.24 ± 0.04 mg/kg at the Control station. All three concentrations exceeded the stated limit of 1.00 mg/kg. The highest Ni concentration occurred at the same station that generally recorded the greatest fish contamination, namely Onosi Okpasimini. Iron concentrations ranged from 32.18 ± 0.61 to 56.74 ± 0.96 mg/kg, and all remained below the stated permissible limit of 100 mg/kg. The high Fe concentration in fish nevertheless demonstrates that Fe is actively present in the aquatic environment and is being incorporated into fish tissue. Ujah et al. (2025) reported a comparable pattern of substantial Fe accumulation in fish from the River Niger, where Fe in fish tissue reached 47.12 ± 0.785 mg/kg at the most affected site. The present concentrations at Obrikom River and Onosi Okpasimini are therefore broadly comparable with recent River Niger observations. IJCCP , Heavy Metal Concentrations in Oreochromis niloticus During Dry Season The dry-season fish results in Table 12 generally show higher concentrations of Pb, Cu, Cr, Cd, Ni and Fe than the corresponding wet-season values at most stations. Pb increased to 3.41 ± 0.08 mg/kg at Obrikom River and 4.26 ± 0.11 mg/kg at Onosi Okpasimini, while the Control station recorded 1.39 ± 0.04 mg/kg. All three values exceeded the stated limit of 0.30 mg/kg. The highest Pb concentration in the dry season therefore occurred at Onosi Okpasimini, consistent with the water results. Copper concentrations were 5.38 ± 0.13, 6.72 ± 0.16 and 2.54 ± 0.06 mg/kg at Obrikom River, Onosi Okpasimini and Control, respectively. These values remained below the stated fish limit of 30 mg/kg, although the impacted stations continued to show higher concentrations than the Control station. Chromium increased during the dry season to 4.71 ± 0.11 mg/kg at Obrikom River and 5.68 ± 0.14 mg/kg at Onosi Okpasimini, while the Control station recorded 2.08 ± 0.05 mg/kg. All values remained above the stated 1.00 mg/kg limit. This persistence of elevated Cr in fish across both seasons suggests sustained environmental exposure. Cadmium recorded 0.57 ± 0.03 mg/kg at Obrikom River and 0.76 ± 0.04 mg/kg at Onosi Okpasimini, compared with 0.10 ± 0.01 mg/kg at the Control station. The two impacted stations therefore exceeded the stated Cd limit of 0.20 mg/kg. This is particularly significant because Cd is a non-essential metal capable of accumulating in organisms following chronic environmental exposure. Nickel also remained above the stated fish limit at the two impacted stations, recording 3.16 ± 0.08 mg/kg at Obrikom River and 3.79 ± 0.10 mg/kg at Onosi Okpasimini. Iron increased to 54.72 ± 0.91 and 64.83 ± 1.04 mg/kg, respectively, but remained below the stated limit of 100 mg/kg. The general dry-season increase in fish-tissue concentrations corresponds with the increase observed in the surface-water concentrations. This relationship is consistent with the ecological principle that fish can accumulate metals from the surrounding water, suspended particles, sediments and food. Recent research emphasizes that the degree of metal accumulation in freshwater fish is influenced not only by ambient concentration but also by species characteristics, age, sex, parasites, tissue type and environmental conditions (Brázová et al., 2025). Consequently, the higher concentrations observed in O. niloticus from Onosi Okpasimini should be interpreted as evidence of greater environmental exposure rather than as proof that water concentration alone determines tissue accumulation. Heavy Metal Concentrations in Soil During Wet Season The wet-season soil results in Table 14 show that Onosi Okpasimini recorded the highest concentrations of Pb, Cu, Cr, Cd, Ni and Fe. Pb ranged from 8.36 ± 0.18 mg/kg at the Control station to 24.67 ± 0.42 mg/kg at Onosi Okpasimini, while Cu ranged from 12.18 ± 0.21 to 28.54 ± 0.35 mg/kg. Chromium ranged from 16.43 ± 0.29 to 38.62 ± 0.51 mg/kg, whereas Cd ranged from 0.21 ± 0.02 to 1.08 ± 0.06 mg/kg. Nickel and Fe showed similar spatial patterns, with maximum values of 22.48 ± 0.39 and 758.62 ± 9.17 mg/kg, respectively, at Onosi Okpasimini. With the exception of Cd at Onosi Okpasimini, the concentrations remained below the stated DPR limits. The relatively high Fe concentration is not unexpected because Fe is naturally abundant in soils and sediments. However, the consistent enrichment of all metals at Onosi Okpasimini compared with the Control suggests an additional anthropogenic contribution. Soil or sediment can act as a long-term reservoir for heavy metals because metals may become associated with clay minerals, iron and manganese oxides, organic matter and other particulate phases. This relationship between water, solid phases and fish is particularly important for interpreting the present findings. Heavy metals introduced into aquatic systems do not necessarily remain dissolved in the water column. They may adsorb onto suspended particles, settle into bottom IJCCP , deposits and subsequently become available to benthic organisms and fish through food-web transfer. A recent Nigerian study in the River Niger similarly found site-specific variation in heavy metals across water, sediment and fish, demonstrating the interconnected behaviour of metals across environmental compartments (Ujah et al., 2025). Heavy Metal Concentrations in Soil During Dry Season The dry-season soil concentrations generally increased relative to the wet-season values. Pb increased to 22.76 ± 0.38 mg/kg at Obrikom River and 29.83 ± 0.47 mg/kg at Onosi Okpasimini, while Cu increased to 25.84 ± 0.32 and 33.76 ± 0.41 mg/kg, respectively. Chromium increased to 36.82 ± 0.51 mg/kg at Obrikom River and 44.73 ± 0.58 mg/kg at Onosi Okpasimini. Cadmium recorded 0.86 ± 0.05 mg/kg and 1.27 ± 0.07 mg/kg at the two impacted locations, respectively, exceeding the stated limit of 0.80 mg/kg. Nickel increased to 20.48 ± 0.36 mg/kg at Obrikom River and 26.73 ± 0.43 mg/kg at Onosi Okpasimini, while Fe increased to 742.63 ± 9.14 and 826.47 ± 10.26 mg/kg, respectively. The consistent increase in soil concentrations during the dry season corresponds with the seasonal increase observed in water and fish. The dry-season enrichment may result from reduced dilution, increased exposure of contaminated surfaces, changes in redox conditions and concentration of previously deposited materials. It may also reflect the remobilisation of metals from contaminated particulate material. Recent research on heavy-metal contamination in aquatic environments continues to demonstrate the importance of examining water, sediment and biota together rather than considering any single environmental compartment in isolation. For example, the 2026 Bonny River study assessed water, sediment and O. niloticus simultaneously and found substantial contamination in water together with Pb and Cd exceedances in tilapia. Bioaccumulation of Heavy Metals in Oreochromis niloticus The bioaccumulation factor results provide important evidence concerning the ability of Oreochromis niloticus to accumulate metals from its surrounding aquatic environment. A BAF greater than 1 generally indicates that the concentration of a contaminant in an organism exceeds its concentration in the environmental medium used for the calculation, suggesting significant accumulation, whereas values below 1 indicate comparatively limited accumulation from that medium. The present results show that Pb and particularly Cd had the strongest accumulation tendencies in O. niloticus. During the wet season, the BAF for Pb was 1.67 at Obrikom River, 1.45 at Onosi Okpasimini and 1.07 at the control. All three values were above unity, indicating that O. niloticus accumulated Pb at all sampling locations. The dry-season BAF values of 1.56, 1.49 and 1.12 at Obrikom River, Onosi Okpasimini and the control, respectively, also remained above 1. This finding is particularly important because Pb concentrations in fish were simultaneously above the stated DPR limit of 0.30 mg/kg at both impacted locations. The results therefore demonstrate that elevated environmental Pb availability is being reflected in fish tissues. The BAF of Cu was below 1 at all locations during both seasons, ranging from 0.80 to 0.82 during the dry season and from 0.81 to 0.82 during the wet season. This indicates relatively limited bioaccumulation of Cu in relation to the water concentration used in the calculation. The result may partly reflect the physiological regulation of essential metals such as Cu by fish. Although Cu is essential for normal biological functions, organisms can regulate its internal concentration more effectively than non-essential toxic metals under certain exposure conditions. IJCCP , Chromium also showed BAF values below 1, ranging from 0.75 to 0.80 during the wet season and 0.77 to 0.79 during the dry season. This suggests relatively limited accumulation of Cr compared with its concentration in the environmental medium. Nickel showed a similar pattern, with wet- season BAF values of 0.63, 1.05 and 0.72 and dry-season values of 0.65, 1.06 and 0.76 at Obrikom River, Onosi Okpasimini and the control, respectively. The slightly greater-than-one values for Ni at Onosi Okpasimini indicate that this location may provide conditions favouring Ni uptake by O. niloticus. The most striking BAF results were observed for Cd. During the wet season, Cd BAF values were 9.20 at Obrikom River, 3.59 at Onosi Okpasimini and 40.00 at the control. During the dry season, the values were 7.13, 3.62 and 33.33, respectively. These values indicate strong accumulation of Cd by O. niloticus, particularly at the control location where the concentration of Cd in water was extremely low. The very high BAF at the control should, however, be interpreted carefully because BAF is a ratio, and a very low denominator can produce an exceptionally high value even where the absolute concentration of Cd in fish is comparatively low. Thus, the BAF should be interpreted alongside the actual fish concentration rather than as evidence that the control site necessarily represents the greatest absolute Cd pollution. The BAF results are broadly consistent with recent Nigerian research. Ogunbanwo et al. (2025) reported significant uptake of heavy metals by O. niloticus and other fish species from water and sediment in the Sagbo Koji Riverine Community. Their findings showed that Fe and Pb were among the metals displaying notable bioaccumulation, demonstrating the importance of fish as biomonitoring organisms. Similarly, Wakil et al. (2025) detected heavy metals in O. niloticus tissues from Biu Reservoir and reported particular concern regarding Pb and Cd. A recent study of O. niloticus, Synodontis clarias and Clarias gariepinus from Kiri Reservoir also demonstrated species- and season-related differences in heavy-metal accumulation, emphasizing that fish uptake depends on both environmental conditions and biological characteristics (British Journal of Multidisciplinary and Advanced Studies, 2025). Contamination Factor and Pollution Load Index of Water The contamination-factor results provide further evidence of the degree to which individual metals contribute to the overall pollution status of the water. During the wet season, Pb recorded very high CF values of 11.33 at Obrikom River and 16.60 at Onosi Okpasimini, while the control site recorded 7.33. These values indicate that Pb was the dominant contributor to water contamination at all locations. Cr also showed elevated CF values of 3.23 and 4.08 at the two impacted sites, while Ni recorded values of 1.60 and 1.12. Fe showed CF values of 1.45 and 1.32. In contrast, Cu had low CF values of 0.16 and 0.20, while Cd recorded 0.50 and 1.70 at Obrikom River and Onosi Okpasimini, respectively. The dry-season results show a further deterioration in the contamination status of the water. Pb CF increased to 14.53 at Obrikom River and 19.07 at Onosi Okpasimini, while Cr increased to 3.84 and 4.57, respectively. Ni also increased to 1.80 at Obrikom River and 1.32 at Onosi Okpasimini. The CF of Cd increased to 0.80 at Obrikom River and 2.10 at Onosi Okpasimini. These increases agree with the higher measured concentrations during the dry season and reinforce the conclusion that contaminant concentration is intensified during periods of reduced hydrological dilution. The PLI values provide an integrated assessment of the combined effect of the investigated metals. The wet-season PLI values were 1.38 at Obrikom River, 1.80 at Onosi Okpasimini and 0.45 at the control. The impacted locations therefore had PLI values greater than 1, indicating an overall polluted condition, whereas the control location had a value below 1, indicating comparatively low overall pollution. During the dry season, the PLI increased to 1.70 at Obrikom River and 2.08 at Onosi Okpasimini, while the control remained below unity at 0.54. IJCCP , The increase in PLI during the dry season demonstrates that the combined metal burden was greater during the dry period than during the wet period. The consistently highest CF and PLI values at Onosi Okpasimini indicate that this station represents the most contaminated of the investigated water locations. This agrees with the concentration results, where Onosi Okpasimini generally recorded the highest concentrations of Pb, Cu, Cr and Cd. Recent research has also demonstrated the usefulness of pollution indices in identifying aquatic pollution hotspots. A 2026 study of the Bonny River system in Nigeria reported very high contamination factors for Pb, Cd and Cr in water and demonstrated clear differences in contamination between environmental compartments (Boma & Nwoke, 2026). Contamination Factor and Pollution Load Index of Soil The soil CF results present a different picture from the water results. During the wet season, all CF values at Obrikom River were below 1, ranging from 0.22 for Pb to 0.90 for Cd. At Onosi Okpasimini, Cd recorded a CF of 1.35, while Cu, Ni, Fe, Cr and Pb recorded values below 1. During the dry season, Cd increased to 1.08 at Obrikom River and 1.59 at Onosi Okpasimini, while the other metals remained below 1. This indicates that Cd is the most important individual contaminant in the soil compartment based on the calculated CF values. The PLI values provided in the study, however, indicate a much greater overall pollution burden in soil than might be suggested by the individual CF values. The reported wet-season PLI values were 9.88 at Obrikom River, 12.75 at Onosi Okpasimini and 4.81 at the control, while dry-season values increased to 11.59, 14.88 and 5.44, respectively. Based on these reported values, Onosi Okpasimini had the highest overall soil pollution burden, followed by Obrikom River and then the control. The increase from wet to dry season indicates an intensified soil contamination burden during the dry season. The high soil PLI values should be interpreted together with the actual concentrations and CF values rather than independently. In particular, the relatively low individual CF values for most metals indicate that the overall index is strongly influenced by the mathematical treatment and reference values used in its calculation. Recent research has continued to employ PLI as an integrated indicator for identifying areas with multiple-metal contamination and pollution hotspots (Lai et al., 2025). The use of PLI is particularly useful where several metals occur simultaneously because it provides an overall indication that may not be apparent from examining individual metals separately. Taken together, the results demonstrate a clear environmental linkage among water, soil and O. niloticus. The impacted locations generally recorded higher heavy-metal concentrations in water and soil than the control, while fish collected from these locations also showed higher concentrations of several metals. For example, the wet- season Pb concentration in fish increased from 1.18 mg/kg at the control to 2.84 mg/kg at Obrikom River and 3.62 mg/kg at Onosi Okpasimini. During the dry season, the values increased further to 3.41 mg/kg and 4.26 mg/kg at the two impacted locations, compared with 1.39 mg/kg at the control. This parallel pattern strongly suggests that the elevated environmental availability of Pb is contributing to its accumulation in fish. The same relationship was observed for Cd. Wet-season Cd concentrations in fish were 0.46 mg/kg at Obrikom River and 0.61 mg/kg at Onosi Okpasimini, compared with 0.08 mg/kg at the control. During the dry season, these values increased to 0.57 mg/kg and 0.76 mg/kg, respectively, compared with 0.10 mg/kg at the control. Thus, the higher Cd concentrations in water and soil at the impacted locations corresponded with higher Cd burdens in fish. The findings are consistent with the conceptual model in which heavy metals enter aquatic systems through anthropogenic and natural sources, become distributed between the water column and IJCCP , particulate or sediment phases, and subsequently become available to aquatic organisms. Fish may absorb metals directly from water through the gills and body surfaces or indirectly through ingestion of contaminated food, suspended particles and sediments. Recent Nigerian research has provided similar evidence of interconnected contamination among water, sediment and fish. Ogunbanwo et al. (2025) found heavy-metal contamination across water, sediments and fish tissues in the Sagbo Koji Riverine Community, while Wakil et al. (2025) demonstrated that Pb and Cd contamination in a Nigerian reservoir could extend from water and sediment to fish tissues. The results indicate that Onosi Okpasimini represents the principal contamination hotspot, followed by Obrikom River, while the control location consistently showed the lowest concentrations and pollution indices. Pb was the most prominent contaminant in the water based on its high CF values, while Cd showed the strongest tendency for bioaccumulation in O. niloticus. Fe was the most abundant metal in both water and soil, although its CF values were considerably lower than those of Pb in water. The dry season generally produced higher concentrations, higher contamination factors and higher PLI values than the wet season, suggesting that reduced dilution and concentration effects contribute substantially to seasonal metal enrichment. The ecological significance of these findings is strengthened by the fish results. The BAF values above unity for Pb and Cd indicate that O. niloticus can accumulate these metals from its environment. This is particularly important because the measured Pb and Cd concentrations in fish at the impacted sites exceeded the stated DPR limits. Recent studies in Nigeria continue to report similar concerns regarding heavy-metal accumulation in edible fish and emphasize the importance of fish monitoring as a component of aquatic pollution assessment (Ogunbanwo et al., 2025; Wakil et al., 2025). Consequently, the combined evidence from metal concentrations, BAF, CF and PLI indicates that the aquatic ecosystem is experiencing measurable heavy-metal pressure, with Pb and Cd requiring particular attention. The higher contamination observed at Onosi Okpasimini suggests that pollution-control and monitoring efforts should prioritize this location. The transfer of metals from environmental media to O. niloticus also has implications for aquatic ecosystem health and human exposure where fish from the river are consumed. This interpretation is supported by recent studies from Nigerian aquatic environments that have identified heavy-metal contamination across multiple environmental compartments and recommended continuous monitoring because of the potential ecological and food-chain implications (Boma & Nwoke, 2026; Ogunbanwo et al., 2025; Wakil et al., 2025). Conclusion The study established that heavy metals were present in the surface water, Oreochromis niloticus and soil within the vicinity of oil production facilities in Omoku, Rivers State. The concentrations of several metals, particularly Pb, Cr, Cd and Fe, were higher at the oil-production-influenced locations than at the control site, with generally higher concentrations recorded during the dry season. The elevated bioaccumulation factors observed for Cd indicate its greater tendency to accumulate in O. niloticus. The pollution indices further indicated varying degrees of contamination, particularly in the soil and surface water around Onosi Okpasimini. The findings suggest that oil production activities and associated anthropogenic pressures may contribute to heavy-metal contamination of the study environment, with potential implications for aquatic ecosystems, soil quality and human health through consumption of contaminated fish. IJCCP , Recommendations Based on the findings of this study, the following recommendations are made: 1. Heavy metal monitoring should be strengthened in water, soil and fish, with particular attention to Pb, Cr and Cd because of their potential toxicity and capacity to accumulate in biological tissues. Periodic testing of locally consumed fish should be undertaken to identify increasing contamination before it becomes a significant food-safety concern. 2. The BAF, CF and PLI indices should be incorporated into routine environmental assessment programmes. 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